Surv {survival} | R Documentation |
Create a survival object, usually used as a response variable in a model formula.
Surv(time, event) or Surv(time, time2, event, type=, origin=0) is.Surv(x)
time |
for right censored data, this is the follow up time. For interval data, the first argument is the starting time for the interval. |
x |
any S-PLUS object. |
event |
The status indicator, normally 0=alive, 1=dead. Other choices are T/F
(TRUE = death) or 1/2 (2=death).
For interval censored data, the status indicator is 0=right censored,
1= event at time , 2=left censored, 3=interval censored.
Although unusual, the event indicator can be omitted,
in which case all subjects are assumed to have an event.
|
time2 |
ending time of the interval for interval censored or counting process
data only.
Intervals are
assumed to be open on the left and closed on the right, (start, end] .
For counting process data,
event indicates whether an event occurred at the end of the interval.
|
type |
character string specifying the type of censoring. Possible values
are "right" , "left" , "counting" , "interval" , or "interval2" .
The default is "right" or "counting" depending on whether the time2
argument is absent or present, respectively.
|
origin |
for counting process data, the hazard function origin. This is most often used in conjunction with a model containing time dependent strata in order to align the subjects properly when they cross over from one strata to another. |
An object of class Surv
. There are methods for print
, is.na
, and
subscripting survival objects. To include a survival object inside a
data frame, use the I()
function. Surv
objects are implemented as
a matrix of 2 or 3 columns.
In the case of is.Surv
, a logical value T
if x
inherits from
class "Surv"
, otherwise an F
.
In theory it is possible to represent interval censored data without a third column containing the explicit status. Exact, right censored, left censored and interval censored observation would be represented as intervals of (a,a), (a, infinity), (-infinity,b), and (a,b) respectively; each specifying the interval within which the event is known to have occurred.
If type = "interval2"
then the representation given above is
assumed, with NA taking the place of infinity. If `type="interval"
event
must be given. If event
is 0
, 1
, or 2
, the relevant
information is assumed to be contained in time
, the value in time2
is ignored, and the second column of the result will contain a
placeholder.
Presently, the only methods allowing interval censored data are the
parametric models computed by survreg
,
so the distinction between open and closed intervals
is unimportant.
The distinction is important for counting process data and
the Cox model.
The function tries to distinguish between the use of 0/1 and 1/2 coding for
left and right censored data using if (max(status)==2)
.
If 1/2 coding is used and all the subjects are censored, it will
guess wrong. Use 0/1 coding in this case.
with(aml, Surv(time, status)) with(heart, Surv(start,stop,event))